32 Thread support library [thread]
namespace std {
  class shared_timed_mutex {
  public:
    shared_timed_mutex();
    ~shared_timed_mutex();
    shared_timed_mutex(const shared_timed_mutex&) = delete;
    shared_timed_mutex& operator=(const shared_timed_mutex&) = delete;
    
    void lock();                
    bool try_lock();
    template<class Rep, class Period>
      bool try_lock_for(const chrono::duration<Rep, Period>& rel_time);
    template<class Clock, class Duration>
      bool try_lock_until(const chrono::time_point<Clock, Duration>& abs_time);
    void unlock();
    
    void lock_shared();         
    bool try_lock_shared();
    template<class Rep, class Period>
      bool try_lock_shared_for(const chrono::duration<Rep, Period>& rel_time);
    template<class Clock, class Duration>
      bool try_lock_shared_until(const chrono::time_point<Clock, Duration>& abs_time);
    void unlock_shared();
  };
}
The class 
shared_timed_mutex provides a non-recursive mutex with shared
ownership semantics
.The behavior of a program is undefined if:
- it destroys a shared_timed_mutex object owned by any thread,
- a thread attempts to recursively gain any ownership of a shared_timed_mutex, or
- a thread terminates while possessing any ownership of a shared_timed_mutex.